This invention relates generally to color digital cameras, and more particularly to the processing of pixel information generated by the sensor of a color digital camera.
Digital color cameras are used with computer or other digital processing systems. Such cameras include a sensor, optics, preprocessing electronics, and a cable or other communication link to transfer data to the digital processing system. Digital cameras are made by Connectix, Intel, and others.
In a conventional digital camera, the sensor is often a charge coupled device (CCD) that produces electrical image signals corresponding to an object producing or reflecting light onto the sensor. The electrical image signals are then processed and recorded on a storage medium such as a memory card or other computer readable medium.
A problem encountered with digital cameras is that the sensor can become saturated when the light intensity exceeds the intensity saturation limit of the sensor. When the light level is above the saturation level of the sensor, all further video information, other than the saturation information, is lost. In the past, this problem has been addressed by attempting to manipulate the amount of light striking the sensor or adjusting the sensor itself.
Some of the prior art has attempted to utilize a light intensity measuring circuit which processes data from the sensor and controls movement of an iris. The iris closes to restrict the amount of incident light striking the sensor and opens to allow more incident light to strike the sensor. However, the movement of the iris is slow compared to other means of intensity adjustment. Furthermore, due to its mechanical nature, the iris often closes more than necessary or doesn""t close enough, at which point it must be repositioned. The result is slow correction time and fluctuations in brightness, ending in degradation of picture quality. The latter is especially if utilized with video cameras, where the fluctuating brightness is captured. Furthermore, a solitary bright light can cause the iris to close so much that gradation of the dark regions becomes compressed and deteriorated. The same occurs when direct strong light is incident, such as in the case of strong rear lighting.
In a system in which an electric charge corresponding to an amount of light received is accumulated on a photodiode and passed to an n-layer substrate of the sensor, other prior art has sought to draw away excess voltage that flows from the photodiode of the sensor when an excessive amount of light is received. For example, a p-layer is positioned between the photodiode and substrate of the sensor and grounded. This applies a reverse bias voltage to the substrate and p-layer so that a depletion layer is formed between the photodiode and the substrate. Surplus electric charges that overflow from the photodiode, due to an excessive amount of received light, are absorbed in the depletion layer. The voltage of the substrate is then adjusted to accommodate bright and dark scenes. A great disadvantage is that signals from the photodiodes are disrupted in that they must now pass through a layer specifically designed to absorb such signals. Another disadvantage of this is that the voltage of the substrate must be preset based on estimated light conditions, especially disadvantageous for capturing moving video. Another disadvantage is that the voltage of the entire substrate must be changed, not just for the portion receiving the excessively intense light. This results in poor picture quality in that bright areas of light are compensated for but dim spots are not.
Another problem encountered with digital cameras is that picture quality drops as the light intensity falls below a certain level. Furthermore, even images in a dark portion of a scene can be hard to observe if a direct strong light is incident in the scene. The prior art has attempted to correct such problems by monitoring signals from the sensor that have been separated into red, green and blue component signals and have also been gamma corrected. Then, a dark area proportion in a whole picked up image is detected. Next, a portion of the processed original signal is modified to stretch the dark signal region to improve the gradation of the dark area. The processed original signal and the modified signal are combined to output a resultant gradation improved signal. The disadvantage of this prior art method is that separation and gamma correction of the original signal are performed before the dark area is detected. This reduces the accuracy of the detection of the dark area. Further, the dark area is estimated from the processed original signal as a whole, not on a pixel by pixel basis, further reducing the accuracy of the detection of the dark area and making correction of the dark area more difficult.
In the present invention, an electrical signal from a light sensor is monitored to detect an intensity saturation condition of at least one pixel of the light sensor. The intensity saturation condition of the pixel is at saturation upon receiving light with an intensity above a predetermined level and below saturation upon receiving light with an intensity below a predetermined level. The electrical signal is converted to a digital signal. A reserved bit combination is imposed on the digital signal indicating the intensity saturation condition of the pixel. A control signal is transmitted in response to the bit combination of the digital signal to compensate for the intensity saturation condition of the pixel. An analog to digital converter can be utilized to convert the electrical signal to the digital signal. The analog to digital converter may be programmable to receive electrical signals of different intensities from the light sensor.
Monitoring the electrical signal may include determining whether a voltage of an electrical signal from the light sensor is above a predetermined level. Further, the control signal may reset the predetermined level of voltage. The analog to digital converter may form part of an analog to digital circuit that also includes an AND gate and an OR gate.
The electrical signal from the light sensor may include a series of signals scanned from preselected pixels from an array of pixels of the sensor, or may include a series of signals scanned pixel by pixel from the array of pixels of the sensor.
In one aspect of the invention, an integrated circuit may perform the aforementioned actions. The integrated circuit may form part of a camera module. Optionally, the camera module may further include the light sensor, a lens assembly aligned with the light sensor, and a printed circuit board supporting the integrated circuit.
In another embodiment of the present invention, pixel data from an output of a light sensor is monitored to determine a number of pixels at saturation. The number of pixels at saturation are compared to a predetermined threshold number. The light sensor is reprogrammed to adapt to more brightness if the number of pixels at saturation is above the threshold number. The light sensor may also be programmed to adapt to less brightness if the number of pixels at saturation is below the threshold number.
A saturation detector may be coupled to the light sensor for detecting an intensity saturation condition of the light sensor. The saturation detector can be reprogrammed to adapt to more brightness if the number of pixels at saturation is above the threshold number. The monitoring of the pixel data may be performed without disturbing data flow. Optionally, reprogramming of the saturation detector can be performed in predetermined increments.
In yet another embodiment of the present invention, pixel data from an output of a light sensor is monitored to determine a number of pixels near saturation. The number of pixels near saturation are compared to a predetermined threshold number. The light sensor is reprogrammed to adapt to less brightness if the number of pixels near saturation is below the threshold number.
A saturation detector may be coupled to the light sensor to detect an intensity saturation condition of the light sensor. The saturation detector may be reprogrammed to adapt to less brightness if the number of pixels at saturation is below the threshold number. Optionally, reprogramming of the saturation detector may be performed in predetermined increments. The pixel data may also be monitored without disturbing data flow.
In still yet another embodiment of the present invention, pixel data from an output of a light sensor is monitored to determine a number of pixels at saturation and a number of pixels near saturation. The number of pixels at saturation is compared to a predetermined first threshold number and the number of pixels near saturation are compared to a predetermined second threshold number. The light sensor is reprogrammed to adapt to more brightness if the number of pixels at saturation is above the first threshold number. The light sensor is reprogrammed to adapt to less brightness if the number of pixels near saturation is below the second threshold number.
In one aspect of the invention, a saturation detector may be coupled to the light sensor to detect an intensity saturation condition of the light sensor. The saturation detector can be reprogrammed to adapt to more brightness if the number of pixels at saturation is above the first threshold number, and can be reprogrammed to adapt to less brightness if the number of pixels near saturation is below the second threshold number. Optionally, reprogramming of the saturation detector can be performed in predetermined increments. Also, monitoring the pixel data may be performed without disturbing data flow.
In yet another embodiment of the present invention, a saturation detector detects and measures an intensity saturation condition of at least one pixel of a light sensor. The saturation detector emits a digital signal with a reserved bit combination indicating the intensity saturation condition of the pixel. A processor receives and processes the digital signal from the saturation detector and transmits a control signal in response to the digital signal to compensate for the intensity saturation condition of the pixel.
The saturation detector may include a voltage detector for determining whether a voltage of an electrical signal from the light sensor is above a predetermined level. The voltage detector may be programmable such that the control signal resets the predetermined level of the voltage. The saturation detector may include an analog to digital converter for converting an electrical signal from the light sensor into a digital signal for indicating the intensity saturation condition of the pixel. Optionally, the analog to digital converter may be programmable to convert electrical signals of different intensities. Also, the analog to digital converter may form part of an analog to digital circuit that also includes an AND gate and an OR gate
The present invention detects situations where too much light is being received, or too little light is being received. When such conditions are detected, they may be corrected by altering the setting of an ADC and a voltage detector on a preprocessor, and by altering the gamma correction and color correction on a host or digital processor. Such gamma and color correction can take place on a pixel by pixel basis.
An intensity saturation condition for each of the pixels of the light sensor may be detected, and a reserved bit combination may be imposed on an ADC output bus to inform a digital processor of the saturation condition for some or each of the independent pixels. A digital processor can use this information to control the ADC to compensate for the saturation condition.
Because the saturation condition of individual pixels is scanned, gamma and color correction may take place on a pixel-by-pixel basis, providing the advantage of producing excellent picture quality free of excessively bright and dim areas. Further, random sampling may be used to reduce the consumption of electric power.
These and other advantages of the present invention will become apparent to those skilled in the art upon a reading of the following descriptions of the invention and a study of the several figures of the drawing.